This disclosure relates to a limited independent steering device in a steer-by-wire steering system.
Vehicular steer-by-wire systems encourage independency in the steering of a pair of steered wheels. In such a steering system, the position of each wheel is controlled by a computer controlled electro-mechanical actuator dedicated to that wheel. The purpose of the independency of the steered wheels is to allow greater capability in the dynamic control of the vehicle. This is accomplished by making steering commands directed to the pair of steered wheels independent of one another. However, it is desirable that a steer-by-wire system possess redundant steering capabilities in the event of the failure of an electro-mechanical actuator. This may be accomplished by a device interconnecting two actuators, which is activated in response to such a failure, and thus shifts or transfers the xe2x80x9cloadxe2x80x9d or steering responsibility of the inoperative actuator to the remaining, operative actuator. This allows the operative actuator to take command of both of the steered wheels.
It is also desirable that such a device be capable of maintaining the aforesaid independency while the vehicle is being operated in its normal mode, i.e., when both actuators are fully operational. This may be accomplished by including a free motion displacement capability within the device. However, the aforesaid independency is lost when command is shifted or transferred from an inoperative to an operative electro-mechanical actuator.
Described herein is a device for transferring steering responsibility from a first electro-mechanical actuator to a second electro-mechanical actuator comprising a cylinder and a first piston slideably disposed within the cylinder. The first piston includes an interior chamber. A second piston is slideably disposed within the interior chamber of the first piston. The device further comprises a first locking sleeve disposed within the interior chamber, a second locking sleeve disposed within the interior chamber in opposition to the first locking sleeve, a first spring disposed within the interior chamber interposed between the first locking sleeve and the first piston and a second spring disposed within the interior chamber interposed between the second locking sleeve and the first piston. The first piston further includes at least one recessed groove juxtaposed to the interior chamber. The first and second locking sleeves each also include at least one recessed groove capable of being brought into alignment with and opposition to the aforesaid at least one recessed groove of the first piston. The second piston also includes at least one recessed groove also capable of being brought into alignment with and opposition to the aforesaid at least one recessed groove of the first piston. The aforesaid recessed grooves of the first and second locking sleeves and second piston each include a snap ring intimately engaged therewith such that upon actuation of the device, the snap rings deploy and are captured by the recessed grooves of the interior chamber, thus locking one of the first or second locking sleeves and the second piston into place within the interior chamber. Such locking of the first or second locking sleeves and the second piston is thereby effective in transferring steering responsibility from a first electro-mechanical actuator to a second electro-mechanical actuator. The device may also include a fluid that acts as damping mechanism.
A method of transferring steering responsibility from a first electro-mechanical actuator to a second electro-mechanical actuator includes slideably disposing a first piston in an interior chamber of a cylinder, slideably disposing a second piston within the interior chamber of the first piston and allowing the first piston to move freely within the cylinder, allowing the second piston to move freely within the first piston, and allowing the first and second piston to be locked together, thereby transferring steering responsibility from a first electro-mechanical actuator to a second electro-mechanical actuator.